As the light source of the projection display device, a discharge lamp such as an ultra high pressure mercury lamp or a metal halide lamp is used. The temperature of the discharge lamp becomes very high during lighting. In particular, when the temperature of a luminous tube becomes equal to or more than a predetermined temperature, the life of the discharge lamp may be shortened or flickers may occur. Therefore, to maintain the temperature of the discharge lamp (luminous tube) within a predetermined range, the discharge lamp must be cooled.
One of the known discharge lamp cooling methods is an air-cooling method that uses a cooling fan. According to the general air-cooling method, the number of revolutions of the cooling fan is controlled according to the increase or decrease of the output of the discharge lamp. Specifically, the number of revolutions of the cooling fan is increased when the output of the discharge lamp increases, and decreased when the output of the discharger lamp decreases. Patent Literatures 1 and 2 disclose more specific cooling fan revolution-number control methods.
Patent Literature 1 describes a liquid crystal display device configured such that the power source of the light source and the number of revolutions of the fan are controlled based on the result detected by a temperature sensor or a light amount sensor. In this liquid crystal display device, the temperature or emission amount of the lamp is detected by the sensor, and fed back to a microcomputer. The microcomputer increases or decreases the number of revolutions of the fan based on the fed-back information.
Patent Literature 2 describes a projection display device configured such that power supplied to the cooling fan is increased when power supplied to the light source is increased, and reduced when the power supplied to the light source is reduced.